The microelectronic industry uses very thin, patterned wafers (e.g., <50 micrometers) in the fabrication of semiconductor devices that require a high level of data processing speed, thereby, leading to the requirement of having a high level of wafer packing, and the ability to perform through-silicon via (TSV) processing and/or withstand wafer grinding. These semiconductor devices are used in many different applications, such as in 3-D packaging and in light emitting diodes (LED). However, since the patterned wafer is very thin, it also tends to be very fragile. Thus the handling of these wafers during the production of a semiconductor device requires processes and materials that are specifically designed to keep the wafer from being damaged. In this respect, temporary wafer bonding and debonding methods have emerged to become a key step in the manufacturing process.
The microelectronic industry currently uses both a one-layer and two-layer approach to accomplish temporary wafer bonding and debonding during the production of semiconductor devices. The basic requirements for temporary wafer bonding include: (i) ability to withstand exposure to at least 180° C.; (ii) ability to survive grinding; (iii) easy to be debonded and cleaned; (iv) high throughput (20-30 wafers/hour); and (v) resistance to many typical chemicals (solvents, acids, bases, etc.) used in semiconductor industry. Spin coating is expected to be used for coating the materials onto the wafers due to the thickness control, simplicity and fast processing that is achievable. A film thickness up to 100 microns with less than 1% thickness variation is required.
The one-layer approach uses a thermal sliding mechanism as described in U.S. Patent Publication No. 2008/0173970. More specifically, a crosslinked oxazoline is used to bond a patterned wafer to a support wafer. After wafer grinding and TSV processing is performed, the wafers are separated by exposing the wafers to a high temperature (285° C.), followed by mechanically sliding the wafers apart. Since the bonding and debonding need to be done at high temperature and harsh solvent cleaning is required to remove any residue, this approach can lead to both low yield and low productivity.
The two-layer approach uses an additional layer to help debond the support wafer from the thin patterned wafer first as described in U.S. Patent Publication No. 2009/0115075. In this approach, a glass support wafer is coated with a thin layer of a thermal sensitive material, e.g., a Light to Heating Conversion (LTHC) material. An adhesive is sandwiched between the LTHC coated glass wafer and a patterned wafer and cured via UV light irradiated through the glass wafer. After wafer thinning and TSV processing is performed, a laser irradiates the stack through the glass wafer to assist in debonding the glass wafer. The adhesive is then peeled off from the patterned wafer. Several disadvantages associated with this approach include the use of both UV and laser sources, the limited lifetime and thermal issues associated with glass support wafers, and the difficulty associated with removing the adhesive from the patterned wafer.
U.S. Patent Publication No. 2010/0330788 describes a thin wafer handling structure that includes a semiconductor wafer, a release layer, an adhesive layer, and a carrier wafer. The structure is bonded together and post bonding processes are performed. The carrier wafer and semiconductor wafer are then separated by applying energy in the form of ultraviolet light or a laser to the release layer. The adhesive on the semiconductor wafer is finally removed by a chemical soaking operation. One disadvantage associated with this approach is related to the cost and difficulty associated with using a UV or laser source to debond the wafers after post-bonding processes are performed.
U.S. Pat. No. 7,482,249 describes the application of a thin layer of a silicon-based material (about 1000 Angstroms) onto a patterned wafer and a solvent-free silicone material (approximately 100 microns) onto a support wafer. The coated patterned wafer is treated with plasma to modify the surface property to improve the compatibility of the release layer material with the silicone adhesive material prior to a bonding step. The bonded wafers are heated to high temperature in order to cure the adhesive. After wafer processing, the thin patterned wafer is attached to a dicing type and removed from the adhesive by taking the advantage of the anisotropic adhesion property of the release layer. In this approach, the coated materials remain to be liquid after being applied to the wafers, making it difficult to manipulate or handle during subsequent processing. In addition, the materials need to be plasma treated, making the process complicated and cost ineffective.